The present invention relates to an optical element formed of a thin film, and an optical switch including the optical element.
An optical switch in which a minute mirror is moved by an actuator and is inserted into an optical path, thereby to change-over the optical path, is described in, for example, the Japanese Patent Application Laid-open No. 2001-42233. With the optical switch, a movable electrode plate on which the minute mirror is mounted is formed by micromachining technology. The minute mirror has a reflective surface which is perpendicular to the principal plane of the movable electrode plate. A fixed electrode is arranged at a position opposite to the movable electrode plate, and a voltage is applied between the movable electrode plate and the fixed electrode, whereby the movable electrode plate is moved by an electrostatic force. Thus, the minute mirror is inserted into the optical path or taken out of the optical path.
With the optical switch described in the Japanese Patent Application Laid-open No. 2001-42233, in order to form the mirror on the movable electrode plate, a photoresist film which has a thickness corresponding to the height of the mirror is formed on a thin film which is to become the movable electrode plate, an etching hole in the shape of the mirror is provided in the photoresist film, and a metal film is grown within the etching hole by plating, whereupon the photoresist film is removed.
Also the Japanese Patent Application Laid-open No. 2001-142008 discloses an optical switch in which a minute mirror is mounted on an actuator and is moved into an optical path by the actuator, thereby to change-over the optical path.
Besides, Sensors and Actuators A, 33 (1992) 249–256, “Microfabricated Hinges” discloses that a film to serve as a plate is formed on a substrate, and that the plate is raised up perpendicularly to the substrate, thereby to form the plate which is perpendicular to the substrate. In a process which forms the film to serves as the plate, a hinge structure which joins one end part of the plate and the substrate is formed. The plate is raised up about the hinge, thereby to finish up a minute vertical structure.